This invention relates to the extracorporeal treatment of blood, and more particularly to the Renal Replacement Therapy or Artificial Kidney.
1. Mechanical Fluid Removal Therapies
Different modalities of Continuous Renal Replacement Therapy (CRRT) have been used to treat patients suffering from excess fluid overload and acute renal failure. In the acute setting, CRRT has been performed previously using standard methods of hemodialysis and continuous arterio-venous hemofiltration (CAVH). More recently, continuous veno-venous hemofiltration (CVVH) has been used to reduce the complications associated with such issues as hemodynamic instability and need for arterial access.
Renal replacement therapy performs two primary functions: ultrafiltration (removal of water from blood plasma), and solute clearance (removal of different molecular weight substances from blood plasma). The filter, also called hemofilter or xe2x80x9cdialyzerxe2x80x9d, can be set up to perform either or both of these functions simultaneously, with or without fluid replacement, accounting for the various modes of renal replacement therapy. xe2x80x9cClearancexe2x80x9d is the term used to describe the removal of substances, both normal and waste product, from the blood.
Ultrafiltration is the convective transfer of fluid out of the plasma compartment through pores in the membrane. The pores filter electrolytes and small and middle sized molecules (up to 20,000 to 30,000 daltons) from the blood plasma. The ultrafiltrate output from the filtration pores is similar to plasma, but without the plasma proteins or cellular components. Importantly, since the concentration of small solutes is the same in the ultrafiltrate as in the plasma, no clearance is obtained, but fluid volume is removed.
Dialysis is the diffusive transfer of small solutes out of a blood plasma compartment by diffusion across the membrane itself. It occurs as a result of a concentration gradient, with diffusion occurring from the compartment with higher concentration (typically the blood compartment) to the compartment with lower concentration (typically the dialysate compartment). Since the concentration of solutes in the plasma decreases, clearance is obtained, but fluid may not be removed. However, ultrafiltration can be combined with dialysis.
Hemofiltration is the combination of ultrafiltration, and fluid replacement typically in much larger volumes than needed for fluid control. The replacement fluid contains electrolytes, but not other small molecules. Since the net effect of replacing fluid without small solutes and ultrafiltration of fluid with small solutes results in net removal of small solutes, clearance is obtained.
2. Limitations of Existing Devices for Ultrafiltration
Dialysis Machines historically used sets of disposables that can be assembled of various parts from different manufacturers. This allowed flexibility in use, but had certain disadvantages. Joints between parts will spring leaks, allowing ingress of air and facilitating clotting. A high degree of skill was required from users to assemble tubes, connectors, filters and accessories and then load them correctly into pumps, bubble detectors, pressure sensors and other interface elements of a dialysis machine. While in the setting of a chronic dialysis center, such practice was acceptable. In the acute setting, such as an Intensive Care Unit (ICU) of a hospital, it became an impediment.
This, among other factors, led to under utilization of mechanical fluid removal in the ICU of a hospital in the past. In the U.S., only recently was the sophisticated apparatus xe2x80x9cPrismaxe2x80x9d from Hospal-Gambro released. This device uses an integrated set where tubing, filter and accessories are all bonded together in the right order and no assembly is required. The filter, sensor interfaces and the four dedicated pump segments (for blood, dialysate, replacement solution and effluent) are also mounted on a flat plastic cartridge to simplify the loading of pumps. The manufacturer advertises the Prisma machine as xe2x80x9can integrated system for continuous fluid management and automated renal replacement therapy blood.xe2x80x9d
Recent changes in the dialysis technology introduced microprocessors, computer graphics interfaces and sophisticated control algorithms. The new generation of controls allows more accurate and safe ultrafiltration. The bases for the advances controls are the sensors. Dialysis equipment uses a variety of sensors that interface with the fluid flow. The sensors include standard configuration pressure sensors, blood leak (typically photometric) sensors and air detection (typically ultrasonic) sensors. Lately, some manufacturers have introduced flow sensors, conductivity sensors, and blood hematocrit sensors.
In all existing dialysis, ultrafiltration and hemofiltration equipment sensors are part of capital equipment. The single use dialysis sets, integrated or not, only include plastic parts with no built in intelligence. Properties of the plastic material as well as mounting conditions contribute to the uncertainty of measurement. For example a 1% accurate pressure sensor can be used to measure blood pressure in the blood return line. Pressure is transmitted from blood through the silicon diaphragm that is a part of the disposable set. Owing to manufacturing methods and properties of the material, the elasticity of the diaphragm has inherent variability of 10%. As a result, practical accuracy of the sensor is dramatically reduced. The sensor to media interface also reduces other performance parameters, such as frequency response, resolution, and stability.
Another noted limitation of the existing dialysis sets is the lack of traceability associated with the single use set. In some countries, dialyzers (the most expansive component) are reused, but sets of tubing are always disposable. All disposable sets have serial numbers and limited shelf life. It is the responsibility of the user to ensure that the serial number of the set is recorded, and that the set is not reused or kept out of the package and on the machine longer than is safe. Yet another limitation of the existing single use dialysis set technology is that it can be easily replicated by xe2x80x9cafter marketxe2x80x9d manufacturers after the original equipment manufacturer has invested in development. This way, dialysis equipment manufacturers have no means of preventing users from using sets that are made by competitors. There is also an associated danger of an incompatible or partially compatible set being used without the knowledge of the manufacturer of the capital equipment.
Digital technologies allow easy storage of significant amounts of digital information in relatively inexpensive miniature ROM (Read Only Memory) chips. In recent years the medical disposables technologies are making increasing use of them. There have been several devices where the disposable component of a medical device has an integral or added xe2x80x9cmemoryxe2x80x9d component. For example, U.S. Pat. No. 5,720,293 discloses a diagnostic catheter with a memory chip where calibration, patient and serial number information can be stored. Camino Neural Care of San Diego, Calif. manufactures a disposable intra-cranial pressure catheter for use in neurosurgery that comes with an individually programmed memory xe2x80x9ckeyxe2x80x9d that contains calibration information for the pressure sensor. None of the aforementioned devices addresses specific needs of an advanced dialysis set.
The present invention is a new and improved integrated disposable set with a memory device for storing useful information used in a dialysis or ultrafiltration set to improve accuracy of sensors, prevent reuse and incorrect use and to protect the set from replication and selling by competitor.
It is an object of the present invention to address the needs of fluid removal and dialysis in the acute and emergency settings. It is another object of the present invention to eliminate significant limitations of existing fluid removal and dialysis devices.
The present invention is directed to a memory device that is used with a disposable ultrafiltration set for dialysis or fluid removal in fluid overloaded patients. The memory device or xe2x80x9ckeyxe2x80x9d is preferably an EEPROM that is embedded in a blood circuit sensor used with the ultrafiltration set or a separate key code card that is plugged into the control panel of the set.
The key can contain information about the manufacture and/or use of the disposable ultrafiltration set, including:
Set Model Number;
Serial number;
Encoded Date of manufacture;
Encoded Expiration date of the set;
Proprietary secret code to prevent unauthorized duplication of a circuit;
Calibration coefficients for single use pressure sensors that are the part of the set;
Calibration coefficients for single use blood optometric leak detector that is the part of the set;
Calibration coefficients for the single use optical oximery sensor (SvO2) that is the part of the set; and/or
Encoded checksum of above data.
Patient data and operational information can be stored in the key during treatment.
The key can also store information written into the key relating to treatment of a patient:
Date and time when the circuit was mounted on the machine;
Machine serial number and model number;
Machine CPU software revision;
Machine hardware revision;
Date and time when the treatment started;
Duration of treatment;
Treatment modality (SCUF, CVVH, CVVHD etc.);
Alarms;
User actions;
User settings such as blood flow, fluid removal rate;
Actual sensor readings such as circuit pressures, blood and other fluid pump flows, oxygen and other gas contents of blood, hematocrit, venous blood pressure when the pump is stopped;
Total amount of fluid removed per treatment;
Date and time when the circuit was dismounted; and
Battery operation.
Preferably the key is returnable to the manufacturer or usable by a hospitable so that information stored in the key can be entered into databases usable for various objectives.